In a so-called virtual shopping mall where many virtual shops open through the Internet, an item category (which is also referred to hereinafter simply as “category”) is often assigned to an item available in each shop. By sorting items into item categories, a manager of the virtual shopping mall can systematically manage an enormous amount of items that are put into stock by the respective shops based on their original sales plan, and further a user can search items of different shops at a time using a category and compare them. For example, a commodity transaction system disclosed in the following Patent Literature 1 has a plurality of search databases corresponding to a plurality of categories representing the types of items. In this system, with each search database corresponding to each category, specification information of items in the category and everyday life words representing the features of the items are associated.